Pulse-echo acoustic ranging systems are widely used to recognize the presence of an object by measuring the time interval between the transmission of sonic or electromagnetic pulse towards the object and the reception of reflected echo signals over a distance. Systems of this kind generally have a transducer serving the dual role of transmitting and receiving pulses, and a signal processor for detecting and calculating the position or range of the object based on the transit times of the transmitted and reflected signals.
The transducer employed in a pulse-echo ranging system typically includes an electro-mechanical vibrating element that functions as both a transmitter and a receiver. Using the same transducer for transmitting as well as receiving is advantageous because the transducer will exhibit the same resonance frequency and the same directional characteristics in both transmit and receive modes. In transmit mode, the transducer is excited with an input voltage signal, which results in the emission of a characteristic burst of electromagnetic, i.e. acoustic, energy. In receive mode, the reflected energy or echo pulse causes the resonator element to vibrate and generate a low amplitude electrical signal output.
A primary problem in pulse-echo ranging systems is the susceptibility of the transducer to decay or “ringing down” oscillations of the resonator element as a result of stored energy being released by the transducer after excitation. The ringing down problem tends to severely limit the sensitivity of the transducer to detect a true or actual echo pulse. This loss in sensitivity is particularly acute when the echo pulse has a low amplitude relative to the ring down pulses of the transducer, and also when the reflective surface (i.e. object) is close to the transducer.
Furthermore, during echo pulse detection, there is a finite time delay between the arrival of the echo pulse and the detection of the echo pulse by the resonator element. The effect of this delay known as “ringing up” is to increase the receiver dead time which results in the receive pulse being longer in time than optimally required. The time delay needs to be taken into account in calculating the transit time of the pulse echo signal.
In order to provide accurate readings, the pulse-echo ranging system needs to know the delay between the echo pulse being received and the detection of the echo pulse as an output signal. Accordingly, there remains a need for improved pulse offset calibration techniques in pulse-echo acoustic ranging systems.